Many attribute VMware's dominance in virtualization to its strong management infrastructure, and the relatively immature RHEV Manager can't yet match VMware's management systems feature-for-feature at the top end. However, it does include high availability, system scheduler and storage management, as well one particularly key feature: live migration (or what VMware calls VMotion).

Live migration is the ability to move running virtual machines from one host
to another without downtime when the virtual disk files reside on a shared
storage substrate. Microsoft's Hyper-V hypervisor faced criticism when it launched
precisely because it lacked a live migration feature, so it is not at all surprising
Red Hat included the functionality at launch.

Two features VMware offers that RHEV Manager lacks are the ability to carry out the live migration of virtual disk files  what VMware calls Storage VMotion  and functionality similar to what VMware Consolidated Backup delivers. But it's a problem Red Hat plans to put right. "We don't have Storage VMotion yet, but we have it on our roadmap, and we don't have an equivalent to VCB right now, but that will change," said Navin Thadani, Red Hat's senior director, virtualization business. When it comes to a VCB equivalent, he said it's not necessary yet because most customers are happier to back up their virtual machines in the same way they back up their physical machines, using backup agents running in the virtual machines. However, agents running on virtual machines can hog resources of the physical hosts during backups, and as virtual machine usage increases it's likely Red Hat customers will begin demanding agentless solutions. "We are talking with our partners, and we will have something like VCB in the future. You will be able to do an apples-for-apples feature comparison between us and VMware," he promised.

The KVM Advantage

Two areas where Thadani said he believes Red Hat's KVM-based virtualization currently has an advantage over VMware are price and application support. Exact costs depend on the number of hosts and machines being virtualized, as well as the operating systems concerned. However, using RHEV instead of VMware could result in between 40 percent and 80 percent costs savings, he claimed. Red Hat guarantees that, because RHEV is built from the same kernel as RHEL, any Linux application that runs on RHEL will also run in a RHEL virtual machine virtualized on RHEV. If it doesn't run properly in this way, Thadani said Red Hat will provide support to fix it so that it does.

Red Hat is finding success competing with VMware in instances where organizations have been running RHEL guests on VMware's platform, he claimed. Some of these organizations are taking these RHEL guests and virtualizing them on hosts running RHEL-with-KVM  on which they get unlimited guest licenses. Applications like SAP, Oracle and DB2 run in a virtualized environment like this at about 85 percent to 95 percent of the performance level they attain when running on RHEL on bare metal, Thadani said.

Customers are also running a mix of Windows and RHEL guests on RHEV, and the motivation for this is to reduce their dependence on VMware, Thadani said. "They are looking for an alternative for VMware, and with RHEV they are finding a credible one. These customers want to maintain a second option to VMware."

As well as planning to introduce features such as Storage Live Migration and consolidated backup in future versions of the management component of RHEV, new capabilities are planned for the hypervisor part by rebasing it on the RHEL 6 kernel, which will probably be released some time this year. Thadani implied this will enable RHEV to leverage SELinux features, more than is currently the case. "It will allow us to secure the hypervisor in a way that is very robust," he said. "It will be possible to make very fine-grained security policies, which will make the hypervisor harder to break into, and even if that happens, it will be nearly impossible to do anything to any virtual machine." The CFS (Completely Fair Scheduler) in RHEL6 will also enable administrators to set exact SLAs for certain virtual machines by guaranteeing them minimum CPU, memory or I/O resources. "This will enable companies to move big, mission-critical applications to an internal cloud," said Thadani.

RHEV and RHEL-with-KVM clearly still have a long way to go before they can compete on equal terms with the entire VMware ecosystem. But Red Hat appears determined to plug away at its virtualization offering, slowly filling in the management features and narrowing the gap until it is ready to go toe-to-toe and slug it out with VMware.

Paul Rubens is a journalist based in Marlow on Thames, England. He has been programming, tinkering and generally sitting in front of computer screens since his first encounter with a DEC PDP-11 in 1979.